High Data Rate (HDR) is an emerging mobile wireless access technology that enables personal broadband Internet services to be accessed anywhere, anytime (see P. Bender, et al., “CDMA/HDR: A Bandwidth-Efficient High-Speed Wireless Data Service for Nomadic Users”, IEEE Communications Magazine, July 2000, and 3GPP2, “Draft Baseline Text for 1xEV-DO,” Aug. 21, 2000). Developed by Qualcomm, HDR is an air interface optimized for Internet Protocol (IP) packet data services that can deliver a shared forward link transmission rate of up to 2.46 Mbit/s per sector using only (1×) 1.25 MHz of spectrum. Compatible with CDMA2000 radio access (TIA/EIA/IS-2001, “Interoperability Specification (IOS) for CDMA2000 Network Access Interfaces,” May 2000) and wireless IP network interfaces (TIA/EIA/TSB-115, “Wireless IP Architecture Based on IETF Protocols,” Jun. 6, 2000, and TIA/EIA/IS-835, “Wireless IP Network Standard,” 3rd Generation Partnership Project 2 (3GPP2), Version 1.0, Jul. 14, 2000), HDR networks can be built entirely on IP technologies, all the way from the mobile Access Terminal (AT) to the global Internet, thus taking full advantage of the scalability, redundancy and low-cost of IP networks.
An EVolution of the current 1xRTT standard for high-speed data-only (DO) services, also known as the 1xEV-DO protocol has been standardized by the Telecommunication Industry Association (TIA) as TLA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification”, 3GPP2 C.S0024-0, Version 4.0, Oct. 25, 2002, which is incorporated herein by reference. Revision A to this specification has been standardized as TIA/EIA/IS-856, “CDMA2000 High Rate Packet Data Air Interface Specification”, 3GPP2 C.S0024-A, Version 2.0, June 2005. Revision A is also incorporated herein by reference.
FIG. 1A shows a 1xEV-DO radio access network 100 with radio network controllers 102 and 104 connected to radio nodes 108, 110, and 112 over a packet network 114. The packet network 114 can be implemented as an IP-based network that supports many-to-many connectivity between the radio nodes and the radio network controllers. The packet network is connected to the Internet 116 via a packet data serving node 106. Other radio nodes, radio network controllers, and packet networks (not shown in FIG. 1) can be included in the radio access network. The packet network 114 may be several distinct networks connecting individual radio network controllers to their associated radio nodes, or it may be a single network as shown in FIG. 1, or a combination.
Typically, each radio network controller controls 25-100 radio nodes and each radio node supports 1-4 carriers each of 1.25 MHz of bandwidth. A carrier is a band of radio frequencies used to establish airlinks with access terminals. The geographic area of the radio access network that is served by any given radio node is referred to as a cell. Each cell can be divided into multiple sectors (typically 3 or 6) by using multiple sectorized antennas (the term “sector” is used both conventionally and in this document, however, even when there is only one sector per cell).
Access terminals, e.g., devices 118, 120, and 122, communicate with the radio nodes of the network 100 over airlinks, e.g., links 124, 126, and 128. Each access terminal may be a laptop computer, a Personal Digital Assistant (PDA), a dual-mode voice/data handset, or another device, with built-in 1xEV-DO Rev-0 or Rev-A support. As 1xEvDO Rev-A is backwards compatible with 1xEvDO Rev-0, Rev-A capable access terminals can operate in either Rev-0 mode or Rev-A mode, depending on whether its serving radio node is Rev-0 or Rev-A capable. A Rev-0 device in communication with a Rev-A radio node will only be able to use Rev-0 services.
When an active access terminal moves from one sector to another, it asks for airlinks on new sectors via Route Update messages. In certain cases, the access terminal may not be able to obtain an airlink on a sector—as a result, the access terminal may remain in communication with the radio node of the sector it is leaving longer (instead of transitioning to the radio node of the sector it is entering). For example, in FIG. 1B, an access terminal 120 has moved from sector 1, where it was in communication with a radio node 110, into sector 2, served by radio node 112. The access terminal 120 is still in communication with the radio node 110 over an airlink 126, instead of establishing a new airlink 130 with the radio node 112. Each radio node transmits a pilot signal to identify itself and inform access terminals of the carriers the radio node uses and which revisions it supports. The access terminal 120 monitors pilot signals in its environment to determine which radio nodes it should establish communication with. An access terminal may be limited in its ability to receive or interpret pilot signals that are transmitted on different carriers or using different revisions than the access terminal is currently using. Likewise it may fail to recognize a pilot signal from a radio node on a different subnet than the radio node with which it is presently communicating. If the access terminal 100 does not recognize that it could use any of the signals it is detecting, or if it fails to detect signals it could use, it may remain in communication with the radio node 110 long after it could have established a better connection to the radio node 112. This condition is referred to as RF Dragging. RF Dragging can cause a degradation in the quality of service the user experiences, for example, a reduced rate of data transmission or an increased number of errors in transmission; in some cases, the connection may be dropped. In such a case, it may be desirable to disconnect the access terminal 120 from the radio node 110 serving the sector it is leaving to force it to transition to the radio node 112 serving the sector it is entering.